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84 Cards in this Set
- Front
- Back
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What are the 2 big things that CONTROL mean arterial pressure?
Which one is fast? Which is slow? |
-Sympathetic activity - FAST
-Renin-angiotensin system - Slow! |
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2 sites of receptors for sensing changes in MAP:
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-Carotid sinuses
-Aortic arch |
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What receptors are in the carotid sinuses?
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-Baroreceptors
-Chemoreceptors |
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What receptors are in the Aortic Arch?
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Same - baros and chemos
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What nerve takes info to the brain from the Aortic arch receptors?
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Vagus
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What nerve takes info to the brain from the Carotid body receptors?
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Glossopharyngeal - Hering's
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Where do these nerves go?
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To the medulla
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What kind of change in MAP do the carotid and aortic arch receptors respond to?
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Aortic - to INCREASES only
Carotid - to both decrease and increases |
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What exactly do Baroreceptors sense?
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Stretch
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What does a decrease in MAP do to the baroreceptors?
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Decreases stretch of Carotid baroreceptors, decreases firing rate of CN 9, and decreases transmission to the medulla vasomotor center.
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To what nature of a decrease will the baroreceptors respond best?
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a RAPID change
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What is the setpoint for MAP in the vasomotor center?
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100 mm Hg
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What happens if the carotids sense MAP below 100 mm Hg?
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Lack of impulses at the vasomotor center stimulate increased symp outflow to raise it back to normal.
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What are the 4 changes that will occur with SNS outflow to restore BP to normal?
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1. Increased HR
2. Increased contractility (SV) 3. Arteriole vasoconstriction 4. VEIN vasoconstriction |
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What does the increased contractility and stroke volume together achieve?
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Increased cardiac output
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What does arteriole vasoconstriction achieve?
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Increased TPR and arterial pressure
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What does VEINoconstriction achieve?
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Shifts blood from the unstressed volume to the stressed volume - increases VR to the heart
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And what does increased VR to the heart achieve?
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Increased Cardiac output and Contractility! Frank Starling!
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What is this sort of baroreceptor reflex useful in?
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Acute blood loss - hemorrhage
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What is the slower, longterm mechanism of BP control?
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RAAS
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How does the RAAS control blood pressure?
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By adjusting BLOOD VOLUME
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What are 3 things that can stimulate Renin release? What is the MAP change that does it?
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-Decreased RENAL PERFUSION PRESSURE sensed by JG cells of the afferent arteriole
-SNS -Low Na in distal tubule sensed by macula densa |
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What are the 2 main actions of Angiotensin II activated by the RAAS?
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1. Global vasoconstriction
2. Stimulates aldosterone synth and release from adrenal cortex |
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What does stimulating Aldo achieve?
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-Increased Na reabsorption
-Increased H2O reabsorption -Increased ECF volume, blood volume, and MAP |
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When is the RAAS response important for increasing MAP?
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In acute hemorrhage it works.
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What is a situation in which you can take advantage of the ability of the carotids to respond to increased MAP? How?
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When you need to slow the heartrate - carotid massage!
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What does carotid massage do?
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Increases stretch, increases firing rate of Hering's nerve, decreases MAP.
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How is Brain Ischemia detected?
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As increases in PCO2 detected by medulla CHEMOreceptors
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What effect does increased CO2 detected in the medulla have?
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Increases SNS outflow to the heart and blood vessels
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WHY would you want to stimulate the SNS if there is DECREASED perfusion of the brain as in ischemia?
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To decrease perfusion to other less vital organs in order to direct it to the brain!
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How MUCH can this reflex to brain ischemia increase MAP?
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Even to life-threatening levels!
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What is this reaction called?
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The Cushing reaction
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What causes the Cushing reaction?
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Increased intracranial pressure which compresses the brain blood vessels, resulting in ischemia and increased brain CO2
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Where are there chemoreceptors other than in the medulla?
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In the carotid sinuses and aortic bodies too.
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What do these peripheral chemoreceptors detect?
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Decreases in PO2 - OXYGEN, not CO2
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What will make the peripheral chemoreceptors stimulate SNS outflow?
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Decreases in PO2
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When is Vasopressin involved in BP control?
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When there is acute hemorrhage leading to low blood volume
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What are the 2 ways by which Vasopressin can increase BP?
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1. Potent VASOCONSTRICTOR
2. Increases water reabsorption |
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What are the receptors that Vasopressin acts on to cause VASOCONSTRICTION? Where?
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V1 receptors - on arterioles
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What are the receptors that Vasopressin acts on to cause Water reabsorption? Where?
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V2 receptors on Principal cells of the distal tubule and CD - in the kidney
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What hormone is released in response to INCREASED MAP?
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ANP - atrial natiuretic peptide
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Where is ANP released from? In response to what?
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The atria - in response to INCREASED MAP
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What are the 3 mechanisms by which ANP can REDUCE MAP?
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1. Relaxes blood vessels
2. Increases Na/H2O excretion 3. Inhibits RENIN secretion |
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What special structure is at the junction of METAarterioles and capillaries?
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Precapillary sphincter
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How is bloodflow through capillaries regulated then?
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By arterioles and these precapillary sphincters
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Where are the clefts between endothelial cells in capillaries
-exceptionally tight -wide and leaky |
Tight - in BBB
Leaky - in liver and intestine |
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What are the wide leaky clefts called in the liver/intestine?
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Sinusoids
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How is fluid exchange across capillaries 'quantified' and calculated?
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With the starling equation - same as in the kidney
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What does the starling equation spit out?
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FLUID FLOW - Jv, in ml/min
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What happens when Jv (flux) is positive?
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There is net mvmt of fluid OUT of capillaries
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Where is Pc higher in capillaries? Where is it lower? Exception?
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Higher - at beginning of bed
Lower - at the end Exception: NOT IN THE GLOMERULUS - it remains constant along its length |
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What is EDRF? Where is it produced?
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Endothelial-derived relaxing factor - made in Endothelial cells
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What does EDRF do?
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Causes local relaxation of vascular smooth muscle
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What is the mechanism by which EDRF causes vasc sm muscle relaxation?
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Activates guanylate cyclase to increase cGMP
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What is a form of EDRF?
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Nitric oxide
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How does ACh cause vascular sm muscle relaxation?
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By stimulating EDRF! ohhhhhh
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So what drug do you never ever give intravenously for the fact that they would cause severe hypotension?
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Bethanechol
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How much CO does the coronary circulation recieve?
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5%
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What is the most/least important control of coronary bloodflow?
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Most = local metabolism
Least = sympathetics |
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What are 2 metabolites produced by the heart that will vasodilate the coronary vasculature?
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-Hypoxia
-Adenosine |
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What 2 metabolites cause cerebral vasodilation?
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-CO2
-H+ |
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What is the most important controller of bloodflow in muscle at rest? When exercising?
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At rest - SNS
Exercising - metabolites |
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What is the major thing to remember about pulmonary bloodflow regulation?
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Hypoxia causes VASOCONSTRICTION
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What is Autoregulation?
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The ability for an organ to maintain normal constant bloodflow over a wide range of perfusion pressures
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What organs exhibit autoregulation?
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Heart, Brain, Kidneys
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What is Active Hyperemia?
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When bloodflow to an organ is PROPORTIONAL to its metabolic activity
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What is an example of Active hyperemia?
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When muscle activity increases, metabolic activity increases, so bloodflow increases Proportionately
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What is REACTIVE hyperemia?
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The increase in bloodflow AFTER A PERIOD OF OCCLUSION
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What is the mechanism that explains AUTOREGULATION?
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Myogenic hypothesis - when vascular smooth muscle is stretched, it contracts to maintain CONSTANT bloodflow.
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What is the mechanism that explains hyperemia regulation of bloodflow?
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METABOLIC hypothesis - when metabolism increases, metabolites are produced that stimulate vasodilation
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What are the 5 main metabolites that cause vasodilation?
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CHOKLA
-CO2 -H -K -Lactic acid -Adenosine |
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What 2 sites is the SNS very important in regulating bloodflow then?
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-Resting muscle
-Skin |
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What are 4 other vasoactive hormones?
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-Histamine
-Bradykinin -Serotonin -Prostaglandins |
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What are the 2 effects of HISTAMINE on the vasculature?
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-Arteriolar vasodilation
-Venous constriction |
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What do these effects combine to do?
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Produce EDEMA
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In what setting do we see histamine cause these effects?
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Tissue trauma
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What does Bradykinin do to the vasculature?
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Same - arteriodilation, venoconstriction
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What does Serotonin do?
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OPPOSITE
-constricts arteries -dilates veins |
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What is Serotonin thought to play a role in?
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Vascular spasms causing migraines
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What are the 4 prostaglandins that affect bloodflow, and how?
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-Thromboxane - constricts
-Prostacylcin - dilates -PG-E - dilates -PG-F - constricts |
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What is the PREDOMINANT controller of coronary circulation?
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METABOLITES
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What are the 2 most important local factors that regulate coronary bloodflow?
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-Hypoxia (O2)
-Adenosine |
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What is the most important local vasodilator for CEREBRAL circulation?
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CO2
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What are the 3 most important local vasodilator substances in skeletal muscle? When do they become important for regulating muscle bloodflow?
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-K, lactate, Adenosine
-In EXERCISE |
